1. Field of the Invention
This invention generally relates to a recording and/or reproducing apparatus and more particularly is directed, but not limited to, a VTR (Video Tape Recorder) wherein a tape is wrapped on the periphery of a head disc and contacts plural heads mounted at the periphery of the head disc to record signals on the tape and/or to reproduce signals from the tape by scanning the heads across the tape in response to the rotation of the head disc.
2. Description of the Prior Art
In a VTR for magnetically recording and/or reproducing video signals by means of magnetic tape, plural heads are mounted on the head disc and the tops of the heads are projected radially from the periphery of the head disc for contacting with magnetic tape wrapped on the periphery of the head disc. Accordingly, the magnetic tape, which is made of polymeric film and has a viscoelastic characteristic, is partially deformed by the projection of the heads beyond the periphery of the head disc as the rotation of the head disc causes the heads to scan across the surface of the tape. These deformations of the magnetic tape move with the heads around the head disc to the position where the magnetic tape is separated from the periphery of the head disc by a tape guide member. The heads apply frictional forces to the magnetic tape from the point where the heads begin to contact the tape to the above mentioned separation point. These frictional forces decrease very rapidly when the above-mentioned heads pass over the separating point. Further, the magnetic tape receives not only the longitudinal tension provided by the tape transport mechanism of the VTR but also a radially directed normal force at the portion of the tape which is wrapped on the head disc. The deformations of the magnetic tape caused by the projection of the heads are quickly removed by this normal force. But the portion of the above-mentioned magnetic tape between the separating point and the tape guide member does not receive such a normal force, and hence the removal of the deformations of the tape caused by the projection of the heads does not occur as rapidly in this portion of the tape as it does at the portion of the tape which is wrapped around the head disc. Accordingly, the magnetic tape vibrates between the above-mentioned separating point and the tape guide member.
Further, air is led into the spaces between the periphery of the head disc and the magnetic tape in response to the rotation of the head disc and this air is discharged at the above mentioned separating point. Hence, the air pressure between the tape and of the head disc at this discharging point is lower than the atmospheric pressure, and the magnetic tape projects or is curved radially toward the center of the head disc at this location. When this projected portion of the magnetic tape is struck by the heads it is pushed out from the head disc, causing vibration. The vibration of this portion of the magnetic tape away from and toward the periphery of the head disc is converted into longitudinal vibration of the magnetic tape upon the periphery of the head disc. Such longitudinal vibration causes time base errors, which appear as flickers on a reproduced picture.